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Invertebrates

By far the most abundant record of invertebrates in the Glen Canyon is trace fossils. Trace fossils are any record of an organism's existence that does not involve an actual body or body part. Burrows and tracks are two of the most common types of trace fossils, but there are many, many kinds.

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Tunnels

In one area, a dark layer of rock about six inches thick runs through white sandstone. When pieces of it break free and weather, a complex system of tunnels is exposed (see left). These tunnels were made by invertebrates, probably some kind of arthropod, and their density shows how abundant life could be at times.

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Tracks

On the surface of a fossil sand dune are the tracks of a large scorpion, shown in the photo on the left (larger version below). When scorpions walk, all four legs on each side end up in roughly the same place, and the impressions sometimes overprint each other, which is why the tracks kind of look like they have toes. The leg spread on this trackway is about four inches (10 cm). When these tracks were discovered, the paleontologists who found them tried to do some research, to see if they could extrapolate the size of the scorpion from how far apart its feet were. Unfortunately, what little data there is suggests that the leg spread does not correlate very strongly with body length, so in the end, we have no better idea of how big this Jurassic scorpion was than we did when we discovered it.

An entire scorpion trackway found preserved on a dune face in the Glen Canyon Formation.

National Park Service

National Park Service

Body Fossils

The only invertebrate body fossils found so far have been little freshwater snails. In the “AncientDesert” section, we described the limestone mounds that seem to indicate the presence of springs. By itself, this doesn’t tell us much about the quality of the water that was coming out; springs can provide water that is fresh or salty, cloudy or clear, and full of dissolved minerals that may or may not be toxic to life. But near these spring mounds, we found impressions of these snails. Not only are they the first snails found in the Glen Canyon Sandstone—which is already a big deal—but they are freshwater snails, which tells us that at least some of the interdunal wet areas were fed by freshwater springs.